This invention relates to clutches, especially for automobile vehicles. More particularly, the invention relates to diaphragm clutches which comprise a reaction plate adapted to be rigidly fastened to a first shaft which is generally a driving shaft, a friction disc mounted for axial movement in relation to the reaction plate and adapted to be rotationally fixed to a second shaft which is generally the driven shaft, a pressure plate mounted for axial movement in relation to the reaction plate, a generally annular cover adapted to be fixed by its outer periphery to the reaction plate and to be rotationally fixed to the pressure plate, a generally annular diaphragragm having a peripheral portion forming an elastic washer of the Belleville washer type for acting on the pressure plate, and a central portion divided into radial fingers for engagement with a movable control element known as the clutch release bearing, and connection means pivotally fastening the diaphragm to the cover, the connection means extending through passages provided in the diaphragm between the radial fingers thereof in the zone in which these fingers are connected to the peripheral portion forming the elastic washer of the diaphragm.
In the construction of clutches of this kind, it is customary to build separately a first sub-assembly composed of the cover and the diaphragm carried by the cover, and a second sub-assembly composed of the pressure plate and fasteners adapted to connect the pressure plate to the cover; these sub-assemblies are then joined together, and the complete unit is then mounted on the reaction plate after insertion of the friction disc.
The present invention relates in particular to the first of these sub-assemblies, that is the assembly formed by the clutch cover and the diaphragm carried by it, but it also relates generally to diaphragm clutches, whether constructed by joining together two preassembled subassemblies or by the sequential assembly of its various component parts.
It has already been proposed to interpose a supporting washer between the diaphragm and the connecting means which pivotally fasten it to the cover, these connecting means bearing against the supporting washer on a circumference of a diameter smaller than that of the circumference on which the supporting washer bears against the diaphragm.
This arrangement has the effect that in the connecting means fastening the diaphragm to the cover a lever action is introduced between the support of these connecting means on the cover and their support on the diaphragm.
However, in arrangements of this type known up to the present time the supporting washer extends radially both inwardly and outwardly beyond the connecting means which apply it against the diaphragm, so that these connecting means must pass through passages provided for the purpose in the supporting washer.
Wheter these connecting means are composed of generally cylindrical pillars or of relatively flat, thin claws, this gives rise in all cases to a certain complexity during assembly, because of the accurate positioning required when the supporting washer is installed, in order to align and engage its passages with the connecting means.
Furthermore, these connecting means do not in themselves have any capacity for axial elasticity, and consequently, as the wear of the diaphragm and of the supports between which it is mounted for pivoting progresses, an increasing amount of play occurs between the diaphragm and these supports.
This play gives rise to a number of disadvantages.
Firstly, it may be the cause of noise. Secondly, during declutching it has the result of introducing a time lag between the moment when the clutch release bearing acts on the radial fingers of the diaphragm and the moment when the peripheral portion of the diaphragm releases the reaction plate.
Finally, the most serious disadvantage is that the play results in a shortening of the possible withdrawal stroke of the pressure plate, so that a declutching operation may be incomplete and the synchronising elements in the associated gearbox may be damaged; in addition, increased wear of the friction disc which is normally urged by this pressure plate against the associated reaction plate occurs.
In order to eliminate certain of these disadvantages, it has already been proposed to provide the supporting washer interposed between the diaphragm and the connecting means with a certain amount of axial elasticity.
However, in constructions of this type proposed hitherto, this supporting washer has in practice a load substantially smaller than the declutching load, that is to say the load of the diaphragm at the position of the clutch release bearing.
Consequently, although this axial elasticity of the supporting washer, which is generally provided in order to attempt to obtain progressivity in the re-engagement of the clutch, can actually enable the diaphragm to be held in the clutch engagement position without play, and therefore makes it possible to eliminate the noise which may normally be caused as the result of the wear inevitably occurring between the diaphragm and its supports, it cannot in any circumstances prevent the time lag in the declutching operation and the reduction of the possible withdrawal stroke of the pressure plate due to this wear, but on the contrary only increases them.
It has in addition been proposed to provide the connecting means fastening the diaphragm to the cover with some axial elasticity by applying during installation of these connecting means a preliminary stress having a higher load than that of the diaphragm at the position of the clutch release bearing.
However, in constructions of this type proposed up to the present time these connecting means bear directly on the diaphragm, without the interposition of a supporting washer.
It is an object of the invention to minimise or eliminate the various disadvantages briefly explained above and to provide an assembly which complies in a simple, advantageous manner with the requirements which have to be met for the easy installation and for reliable and quiet operation over an extended period of time of an assembly of this kind.